We have previously established that epsilon-N-trimethyllysine (TML) is a carnitine precursor in Neurospora and the rat; and it now appears from appropriate isotope dilution experiments in Neurospora that the synthesis of TML proceeds stepwise via epsilon-N-monomethyllysine (MML) and epsilon-N-dimethyllysine (DMAL): Lysine yields MML yields DMAL yields TML. We have shown conclusively that the methyl groups of carnitine are derived directly from methionine rather than choline, and conditions will be sought to demonstrate methylation of lysine by S- adenosylmethionine either in cell free extracts or particulate systems. Published work of others on the protein methylases may be useful in this regard. TML has been found to be readily incorporated into gamma- butyrobetaine (gamma-BB) and carnitine in rat liver slices and this system will now be exploited to gain insight into TML yields gamma-BB transformations. In time course studies (liver slice system) a radioactive compound derived from (CH#-H3) TML appears and then decreases with the concomitant formation of carnitine. Identification of this intermediate may yield useful information relevant to carnitine biogenesis. Work will continue on seeking ways to improve the production of a high lysine yeast by fermentation processes with yeast lysine auxotrophs selected to accumulate lysine precursors, or strains of yeast resistant to lysine analogs. Such latter strains may have derepressed levels of critical enzymes in the biosynthetic pathway.